This invention relates to a process for preparing imido ester acid salts and, in particular, relates to an improvement in a process for preparing certain dialkyl propanediimidate dihydrohalides.
McElvain and Schroeder, JACS 71, 43 (1949), disclose the preparation of dimethyl and diethyl propanediimidate dihydrochloride by treating malononitrile and the corresponding alcohol with a large excess of hydrogen chloride using a chloroform-dioxane mixture and dioxane, respectively, as solvents. The process is disclosed to give high yields, but a reaction time of about 24 hours is required.
U.S. Pat. No. 3,402,193, issued on Sept. 17, 1968 to Hagemeyer, Jr. et al. discloses that in a process for the preparation of imido ester hydrochlorides by the reaction of a nitrile selected from the group consisting of alkyl, aralkyl and aryl nitriles having from 2 to 19 carbon atoms, a lower alkanol and hydrogen chloride at a temperature of -10.degree. to 50.degree. C., improved results can be obtained by using in the reaction an excess of the nitrile of not less than 25% of the stiochiometric amount.
U.S. Pat. No. 3,538,139 which issued to Hagemeyer, Jr. et al. on Nov. 3, 1970 discloses that in the process for the preparation of imido ester hydrochlorides by the reaction of alkyl, aralkyl, aryl, alkaryl and aryloxyalkyl nitriles having from 2-19 carbon atoms with a lower alkanol and anhydrous hydrogen chloride at a temperature of -10.degree. to 50.degree. C., improved results can be obtained by contacting the reactants while dissolved in an alkyl ester which has an alcohol moiety corresponding to the alcohol reactant and an acid moiety corresponding to the nitrile reactant.
Improvements in the process for preparing these imido ester hydrohalides are increasingly desirable and are constantly being sought. Furthermore, an improved process which provides both improved yields and shorter reaction times offers even greater attractions.